Hi Monks,

I came across John Guttag's book on computation - "Introduction to Computation and Programming Using Python". Note that I love Perl, but found this book to be very interesting. I tried the second finger exercise and though, initially it appeared trivial to solve, it took me a real long time to figure it out.

Here's the exercise: Write a program that examines three variables— x , y , and z — and prints the largest odd number among them. If none of them are odd, it should print a message to that effect.

Points to note:- This is to be tackled using only if/else loop and comparisons, because that is what the author has covered till that part.

Here's my attempt in Perl. I tried other ways, but most of them would not print the expected results if either of the numbers were negative, or two of the three numbers were even.

use strict;
use warnings;

my ($x, $y, $z) = (-11,-13,4);

if ($x % 2 == 0 and $y % 2 == 0 and $z % 2 == 0) {
    print "All are even numbers\n";
} elsif ($x % 2 == 0 && $y % 2 == 0) {
    print "$z is the biggest odd number\n";
} elsif ($y % 2 == 0 && $z % 2  == 0) {
    print "$x is the biggest odd number\n";
} elsif ($x % 2 == 0 && $z % 2 == 0) {
    print "$y is the biggest odd number\n";
} elsif ($x % 2 == 0 && $y % 2 != 0 && $z % 2 != 0) {
    if ($y > $z) {
        print "$y is the greatest odd number\n";
    } else {
        print "$z is the biggest odd number\n";
    }
} elsif ($y % 2 == 0 && $x % 2 != 0 && $z % 2 != 0) {
    if ($x > $z) {
        print "$x is the greatest odd number\n";
    } else {
        print "$z is the biggest odd number\n";
    }
} elsif ($z % 2 == 0 && $x % 2 != 0 && $z % 2 != 0) {
    if ($x > $y) {
        print "$x is the greatest odd number\n";
    } else {
        print "$y is the biggest odd number\n";
    }
} else {
    if ($x > $y && $x > $z) {
        print "$x is the biggest odd number\n";
    } elsif ($y > $z) {
        print "$y is the biggest odd number\n";
    } else {
        print "$z is the biggest odd number\n";
    }
}
[download]

Update: As pointed out by Choroba, I did a typo at line 26. Sorry for the typo. I've fixed it below.

use strict;
use warnings;

my ($x, $y, $z) = (-11,-13,-17);

if ($x % 2 == 0 and $y % 2 == 0 and $z % 2 == 0) {
    print "All are even numbers\n";
} elsif ($x % 2 == 0 && $y % 2 == 0) {
    print "$z is the biggest odd number\n";
} elsif ($y % 2 == 0 && $z % 2  == 0) {
    print "$x is the biggest odd number\n";
} elsif ($x % 2 == 0 && $z % 2 == 0) {
    print "$y is the biggest odd number\n";
} elsif ($x % 2 == 0 && $y % 2 != 0 && $z % 2 != 0) {
    if ($y > $z) {
        print "$y is the greatest odd number\n";
    } else {
        print "$z is the biggest odd number\n";
    }
} elsif ($y % 2 == 0 && $x % 2 != 0 && $z % 2 != 0) {
    if ($x > $z) {
        print "$x is the greatest odd number\n";
    } else {
        print "$z is the biggest odd number\n";
    }
} elsif ($z % 2 == 0 && $x % 2 != 0 && $z % 2 != 0) {
    if ($x > $z) {
        print "$x is the greatest odd number\n";
    } else {
        print "$z is the biggest odd number\n";
    }
} else {
    if ($x > $y && $x > $z) {
        print "$x is the biggest odd number\n";
    } elsif ($y > $z) {
        print "$y is the biggest odd number\n";
    } else {
        print "$z is the biggest odd number\n";
    }
}
[download]

While this works fine for all the test cases I tried, but I will be thankful if you could please let me know a better way of writing this. Point to note is, it should only use if/else/elsif loops and / or comparison operators.